The aim of this research proposal is to improve our understanding of the role played by theextramitochondrial pathway of fatty acid oxidation. The conditions under which the extra- and intramitochondrial pathways operate will be ascertained. The specificity and selectivity of the extra- and intramitochondrial pathways will be examined with respect to substrate and inhibitors of Beta-oxidation. The systems to be used include the perfused liver, isolated hepatocytes, and cell-free systems containing various combinations of particle-free cytosol, mitochondria, peroxisomes, and microsomes. 2-Bromooctanoate is converted by liver to 2-bromo-3-ketooctanoyl-CoA, a powerful inhibitor of thiolase I. It was shown previously that 0.6 mM 2-bromooctanoate causes complete inhibition of Beta-oxidation, ketogenesis, and gluconeogenesis by the perfused liver. The effects of low doses of the inhibitor, which should cause only partial inhibition of Beta-oxidation, will be examined, as will the effects of homologs and analogs of 2-bromooctanoate. The aim is to achieve selective or partially selective inhibition of the intra- and extramitochondrial pathways of Beta-oxidation. The proposed inhibition studies may provide the rationale for designing drugs that will serve to control the rate of Beta-oxidation of fatty acids and hence of ketogenesis and gluconeogenesis. The extramitochondrial pathway of Beta-oxidation is initiated by fattyacyl-CoA oxidase, located in the peroxisomes. Other extramitochondrial enzymes of Beta-oxidation occur predominantly in the cytosol; thus there is most probably an interplay between the enzymes of Beta-oxidation in mitochondria and particle-free cytosol. These interplays will be examined in cell-free systems containing various combinations of particle-free cytosol, mitochondria, peroxisomes, and microsomes. Studies of the B-oxidation of prostaglandins will provide new insights into the control of the degradation of this important group of hormones. Studies of Beta-oxidation of compounds that undergo w-oxidation will throw light on whether subsequent Beta-oxidation of such compounds occurs in the cy tosol, or mitochondria, or both. A possible role of extramitochondrial Beta-oxidation in the supply of carbon for cholesterol synthesis will be investigated.